This invention relates to novel Portland cement (hereafter "cement") dust briquettes or pellets (hereafter "briquettes") and process of producing the same. In another aspect, this invention relates to a process of producing cement by recycling into the Portland cement process Portland cement dust which has been recovered in said cement process and converted into said novel briquettes which are then used by recycling the same into the cement kiln with cement-producing ingredients.
In the production of cement, cement dust consisting of very fine particles of partially calcined raw materials is carried out of the kiln by the air velocity existing inside the kiln and the resulting escaping cement dust is either permitted to pollute the atmosphere or is sought to be returned by a recycling process to the kiln. Being finely divided, the reintroduction of the escaping cement dust into a kiln in its original state often does not result in complete calcining of the dust as most of the dust is again carried out of the kiln by the air velocity existing inside the kiln. Therefore, methods of agglomerating, pelletizing or briquetting said escaping dust have heretofore been proposed with the projected purpose of attempting to provide a more efficient method of recycling said dust back into the kiln. Previous methods of recycling the dust include mixing the dust with a slurry feed, feeding the dust into the kiln via scoops located tangentially on the kiln downward the chain section, agglomerating the dust with water or other materials, and insufflating the dust into the burning zone. As a practical proposition, these methods have not provided a satisfactory answer to the problem of recycling Portland cement dust. U.S. Pat. Nos. 2,140,471; 2,477,262; 2,687,290; 3,206,526; and 3,298,843 are illustrative of the foregoing and other approaches which have been disclosed in an effort to meet the problem. In U.S. Pat. No. 3,298,843, a procedure is disclosed in which the amount of cement dust, which forms when conventional kiln operations are carried out to produce cement, is reduced by initially forming compressed molded bodies of calcium oxide and calcium carbonate in certain proportions to each other, with or without binders such as water, alkaline earth metal hydroxides, heavy mineral oils, vegetable oils, spent liquors from paper making processes, and natural and synthetic plastic materials, and the resulting molded bodies are then calcined in a kiln at elevated temperatures.
The present invention provides novel cement dust briquettes and a process for producing the same under certain conditions which include compacting said cement dust under elevated pressures, the resulting briquettes being adapted to be recycled into the cement kiln, along with the cement producing ingredients, or otherwise introduced into the cement kiln in the cement making process. The novel cement dust briquettes of the present invention are characterized by a crushing strength sufficient to avoid undue disintegration or breakdown in handling and feeding the same into the cement kiln as in recycling operations.
In the production of the cement dust briquettes of the present invention, cement dust, which is recovered from the cement kiln in the cement producing process, is compacted under elevated pressure conditions in a mold while simultaneously encapsulating said briquette with a mineral oil or the like, whereby the resulting encapsulated cement dust briquette possesses sufficient crushing strengths so as to permit reintroduction of the briquettes into the kiln without disintegrating into fine dust particles. The briquettes of the present invention, as indicated above, are strong enough to withstand external forces encountered during recycling from the briquette formation area to reintroduction into the kiln, but the briquettes disintegrate in the kiln without allowing a substantial amount of fine dust particles from becoming airborne once again.